Comparison of the age-standardized HI seroconversion rates in paired sera and paired EDTA-plasma.

(A) The 2010 H3N2 influenza season in Hong Kong caused by A/H3N2/Victoria/210/2009. (B) The 2011 H1N1 influenza season in Hong Kong caused by A/H1N1/California/7/2009. Color codes indicate the source of paired specimens used for calculating seroconversion rates: blue indicates paired EDTA plasma from HKRCBTS blood donation archives, while red indicates paired sera from Kwok et al. [20]. Square and circle indicate the conventional (≥4-fold rise and the latter titer ≥1:40) and alternative (≥4-fold rise) definition of seroconversion, vertical bars indicate 95% confidence intervals.